The stabilising function of the mm. iliocostales and the mm. multifidi during walking.

The myoelectric activity of the mm. multifidi and the mm. iliocostales lumborum of six subjects was recorded during walking. The subjects walked on a treadmill as well as on a fixed walkway. On the treadmill, recordings were made at two different speeds and with a varying loading of the spine. There was almost no difference in myoelectric activity time between the treadmill and the fixed walkway. Related to unloaded walking, both the multifidi and the iliocostales showed an increase in activity time when the subjects carried a load of 5 kg in front of the trunk and a decrease of activity time with a load of 5 kg on the back. A load on the lateral aspect of the body shortened the muscle activity time of the multifidi on the homolateral side. In three subjects the same pattern was found for the iliocostales, but in the other three subjects there was no activity registered at all. On the side contralateral to the load, the multifidi showed no increase of activity time while the iliocostales muscles demonstrated an increase. It is concluded that during walking the iliocostalis muscle has a more important function in lateral bending than the multifidus. It was remarkable that the multifidi muscles of the left side were active for longer periods than were those of the right side in all situations except during lateral loading.